中风导致大脑沟通网络分裂


  April 19, 2007 — 空间忽略是中风后失能的一项表现,主要是大脑额顶叶的背根与腹根的沟通网络受损;目前的新发现是,一个区域的受损是如何影响大脑其它部位的运作。
  
  圣路易斯密苏里华盛顿医学大学的研究员于3月15日神经元(Neuron)期刊上发表研究指出,空间忽略症状的严重度与两个主要分离的沟通网络受损程度是相关的。
  
  主要研究员Maurizio Corbetta博士向Medscape表示,空间忽略是一个破坏性的症状,过去几年我们认为它在大脑的扫瞄区域上可看见受损的部位,但是我们发现大脑是高度连结的,因此大脑一个区域的受损不会只影响该区所负责的功能,而会影响大脑远端区域连结的功能。
  
  【关键的机转】
  根据研究,中风所造成的空间忽略,大多与腹根网络受损、而少数与背根有关,但是在2005年Corbetta博士与其同事发表的研究指出,空间忽略在左脑与右脑背根皮质的诱发反应在功能上的失衡,即使这些区域在结构上是完整的。
  
  他表示,发现这些所谓的「距离效应」确实对于病患的功能有影响,那些活化越失衡之病患的空间忽略问题越大;我们也发现,就如他们发现的,左边大脑与右边大脑失衡的程度会改善,且这些病患的「行为功能」也会进步。
  
  在目前这项研究中,Corbetta医师表示,研究者特定地针对腹根网络以及背根网络之间的连结,且可以描述其之间的活性关联。
  
  为了达到这个目的,他们针对11位右半边中风,在中风1个月时与6个月后,造成空间忽略,在进行功能性连结核磁共振造影(FC MRI)时进行视觉空间行为;这些结果显示,背根与腹根专注网络功能连结性的异常构成空间忽视病理生理学上一个重要的机转。
  
  【具有潜力的研究工具】
  这些发现也突显了研究者的网络假设,脑部半球损伤会对维持适当功能所需部分脑部区域造成伤害;需要更多研究决定其它中风引发的缺失,例如失语症,是否会造成相对应脑部区域类似的连结异常。
  
  除此之外,Corbetta医师表示,FC MRI可能最终提供中风病患或是其它脑部损伤或是疾病病患在功能上信息一个有潜力的研究工具;他附带表示,FC MRI也会提供其它好处,其所需时间很短,且可以于病患静止时进行。
  
  他指出,这项技术的好处是我们可以看到网络的运作,即使病患静静地闭着眼睛躺在机器中;这是非常重要的,因为这项新的扫描技术让我们可以针对急性或是非常严重的病患进行扫描,这在之前是无法达到的。

Stroke Damage Disrupts Brain's

By Caroline Cassels
Medscape Medical News

April 19, 2007 — Spatial neglect, a common poststroke disability, has been linked to impaired communication between attention networks in the dorsal and ventral frontoparietal areas of the brain, a finding that generates a new understanding of how damage in 1 region of the brain affects others.

In a study published in the March 15 issue of Neuron, investigators at Washington University School of Medicine, in St. Louis, Missouri, found a consistent link between the severity of spatial-neglect symptoms and the degree of impairment in communication within and between these 2 largely separate communication networks.

"Spatial neglect is a devastating syndrome, and for many years we thought it was solely due to lesions in specific regions of the brain that were visible on imaging scans. However, one of the things we discovered is that the brain is highly interconnected, and as a result, a lesion in 1 part of the brain not only damages the function of the region where it occurs but also affects other distant areas [of the brain] it is connected to," principal investigator Maurizio Corbetta, MD, told Medscape.

Critical Mechanism

According to the investigators, strokes that cause spatial neglect frequently result in structural damage to the ventral network while sparing the dorsal network. However, a study published by Dr. Corbetta and colleagues in 2005 showed patients with spatial neglect have a functional imbalance of evoked responses in the left and right dorsal parietal cortex, even though these areas are structurally intact.

"We found that these so-called 'distant effects' did have an impact on patients' function and that people with more imbalance in their activation have more neglect. We also found that as they recovered, this degree of imbalance between the left side and the right side of the brain also improved and so did patients' behavioral function," he said.

In the current study, said Dr. Corbetta, the investigators specifically looked at the communication between the ventral attention network and the dorsal attention network and were able to describe the correlation of activity between them.

To do this, they had group of 11 patients who had suffered a right hemispheric stroke resulting in spatial neglect complete a visuospatial attention task while undergoing functional connectivity magnetic resonance imaging (FC MRI) at 1 month and again more than 6 months following stroke.

The results "showed that disrupted functional connectivity in the dorsal and ventral attention networks constitutes a critical mechanism underlying the pathophysiology of neglect."

Promising Investigational Tool

The findings also reinforce the investigators' network hypothesis that injury in 1 part of the brain can damage processes between brain regions essential for the regions' proper function.

Further studies to determine whether other stroke-induced deficits, such as aphasia, are linked to similar disruptions of communication between brain regions are planned.

In addition, said Dr. Corbetta, FC MRI is a promising investigational tool that may eventually make it possible to provide a more accurate prognosis in stroke patients or individuals with other types of brain injury or disease based on functional information.

He added that FC MRI also offers other advantages — it takes very little time and it can be done when patients are at rest.

"The beauty of this [technique] is we can see this network even when patients are quietly lying in the scanner with their eyes closed. It doesn't require patients to interact. This is really very important, because this new way of scanning allows us to study acute or very severe patients, something we weren't able to do before," he said.

Neuron. 2007;53:905-918.

    
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